The present invention relates to an electrophotographic color image forming apparatus in which a plurality of charging means, image-wise exposure means and developing means are arranged around a drum-like or a belt-like image forming body, and in which a color image is formed by superimposing toner images on the image forming body during a single rotation of the image forming body.
The following are widely known as multi-color image forming apparatuses. (A): a color image forming apparatus which is provided with the same number of photoreceptors, chargers and developing units as the number of required colors, and in which mono-color toner images respectively formed on the respective photoreceptors, are superimposed on an intermediate transfer body. (B): a color image forming apparatus in which a photoreceptor is rotated plural times, and charging, image-wise exposure and developing for each color are repeated. (C): a color image forming apparatus in which charging, image-wise exposure and developing for each color are successively conducted during single rotation of the photoreceptor.
However, the above-described apparatus (A) has a disadvantage in which dimensions of the apparatus are excessive because of the plurality of photoreceptors or an intermediate transfer body. On the other hand, dimensions of the apparatus (B) are reduced due to only one charging means, image-wise exposure means and photoreceptor, but sizes of the formed image is limited within the surface area of the photoreceptor.
In contrast to the above-described two apparatus, the apparatus (C) has excellent advantages in which the size of the image is not limited and in addition images are formed at a higher speed.
However, the apparatus (C) has the following disadvantages. When a drive gear for transmitting the drive force to the image forming body has uneven pitch or fluctuations of the depth of engagement, the transmission speed is periodically changed and causes the peripheral speed of the image forming body to fluctuate, even though the motor speed is constant. Therefore, registration of the images to be superimposed is changed, and doubling occurs and image quality is greatly lowered.